Reducing CO2-emission is a focus area in many areas of technology nowadays. This applies also to the area of telecommunications. Some telecommunications companies have set up tough goals to reduce CO2-emissions considerably during the next few years. This tough goal applies to the entire product portfolio, including the use phase, where most of the indirect carbon-related impact originates. Thus energy saving in both Radio Base Station (RBS) and User Equipment (UE) of wireless communication systems are examples of activities that are given priority. In case of UE power efficiency, energy saving will also lead to longer battery life time, which is important for the end user experience.
In a radio network, the radio resources over a radio interface are generally controlled by the radio base station for both RBS to UE transmission, i.e. downlink traffic, and UE to RBS transmission, i.e. uplink traffic. Assuming a fixed bandwidth, the maximum data rate that can be provided over the radio interface is limited by the transmit power. However, the bitrate generated by most applications is below the maximum bitrate over the radio interface. The maximum output transmit power will therefore not be used at low to medium cell loads. A scheduler in a radio base station may order the transmitter, i.e. RBS in case of downlink transmission and UE in case of uplink transmission, to transmit application data e.g. immediately after reception, or to buffer the application data until maximum output power can be utilized. Thus the type of scheduling applied will impact the load distribution of the output transmission power. It is generally assumed that the total transmitted energy for transmitting the same amount of data will be more or less the same, independently of the load distribution, provided that the radio conditions between the RBS and the UE are the same. However, measurements performed on a power amplifier of an RBS and of a UE have revealed that this assumption often is false. There is thus a problem that the power consumption for transmitting a certain amount of data may vary depending on the scheduled load distribution, which may lead to poor power efficiency in certain situations.